Mr. F. M'Coy on the I'lacodermi. 277 



The only specimen which I have seen is not in fructification, 

 but is otherwise in a very perfect and satisfactory state. In ge- 

 neral appearance, especially when placed in water, it might be 

 compai'ed to some kinds of Potamoffeton, and probably vegetates 

 in quiet and shallow bays. The vesicles, as may be seen in the 

 plate, form an axillary raceme, and no doubt indicate the position 

 of the fructification, which, in more advanced individuals, would 

 be probably found towards the extremity of the branches. In 

 my specimen I observe no trace of it, although the vesicles are 

 present on every part. 



EXPLANATION OF PLATE V. 

 Sargassum echinocarpum. 



Fig. 1. Portion of a branch. 



— 2. Leaf with a vesicle at its apex. 



— 3. Leaves producing vesicles. 



— 4. Vesicle with foliaceous expansion of the stalk, 



— 5. Vesicle in its simplest form. 



— 6. Receptacles, with a leaf passing into a vesicle. 



— 7. Portion of a raceme. 5 — 7 magnified. 



Sargassum Campbellianum, 



Fig. I. One of the smaller branches. 



— 2. A leaf with raceme of fructification. 



— 3. Vesicle. 



— 4. Receptacles passing into leaves and vesicles. 2 — 4 magnified. 



Sargassum debile. 



Fig. \. Portion of a branch. 



— 2. Leaf and vesicles; the last magnified. 



XXXI. — Reply to Sir Philip Egerton's Letter on the Placodermi. 

 By Frederick M'Coy, M.G.S. & N.H.S.D. &c. 



To the Editors of the Annals of Natural History, 



Gentlemen, 

 I REGRET to have to trouble you with a few lines in reply to the 

 above article in your last Number. The opinion I entertained of 

 the value of your space and the reader's time induced me to con- 

 dense the gradually acquired experience of years into a very brief 

 paragraph, proposing the family Placodermi for certain Ganoid 

 fish, in my paper in the ' Annals ' of July last. This brevity has I 

 fear caused me to have been misunderstood by Sir P. Egerton, 

 who has reprinted the paragraph in his letter, adding, that " Not 

 having seen the specimens which have induced Mr. M'Coy to 

 propose this new classification, I am unable to form any opinion 

 as to whether he is justified or not in making the change.^' I 



